The present invention relates to a treatment method of wastewater containing hazardous matter, and more particularly, to a wastewater treatment method for removing hazardous matter by irradiating electron beam on the wastewater.
Industrial waste derived from today's remarkable industrial development seriously affects natural environment. Further, water pollution due to industrial wastewater threatens potable water resource of mankind, to thereby cause a big social problem such as the ecological destruction in a natural world.
Particularly, heavy metal such as lead (Pb), cadmium (Cd), sexivalent chrome (Cr.sup.6+) and mercury (Hg) and fluorion excess environmental restriction values, and are contained in industrial wastewater.
Such hazardous matter is very injurious to a human being and pollutes the quality of water and soil.
Thus, various methods for removing such hazardous matter have been under study. Among well-known methods for removing hazardous heavy metal, there are a hydroxide precipitation method, a sulfide or carbonate treatment method, and a method using a zeolite or corallite as an adsorbent. However, such conventional methods have the difficulties in processing of the wastewater with general chemicals due to various inhibit materials, and cannot completely process heavy metal due to a large amount of sludges generated in the case of wastewater containing a large amount of heavy metal.
Particularly, a conventional wastewater treatment or removal method for processing wastewater containing Cr.sup.6+ reduces the Cr.sup.6.degree. to trivalent Cr ions (Cr.sup.3+) and precipitates the Cr.sup.3+ under a base circumstance, to thereby remove the Cr.sup.6+. That is, chromic acid CrO.sub.4.sup.2- which is stable under a base circumstance is processed using Ferrous Sulfate (FeSO.sub.4) and sodium sulfite Na.sub.2 SO.sub.3 both of which are reducing agent, and reduced to Cr.sup.3+. Then, pH condition is maintained pH8.5 by sodium hydroxide or calcium hydroxide to thereby precipitate and filter chrome hydroxide. In this case, a process of neutralizing remaining solution and discharging the neutralized solution is additionally required. Thus, this method requires a complicated multiple processing and uses a large amount of chemicals, thereby much costs being required.
Also, a conventional wastewater treatment method for processing wastewater containing bivalent Hg ions (Hg.sup.2+) follows a general heavy metal ion removal method. However, such a general heavy metal removal method is not particularly efficient for removing Hg.sup.2+.
The above heavy metal processing methods require multiple chemical processing so that it needs to take a long processing time. Such methods use a large amount of chemicals, and thus cause processing costs to be high. Also, they do not perfectly remove hazardous heavy metal.
Meanwhile, among conventional methods for removing fluorine from wastewater, there are a metallic salt (generally Ca compound) addition method, a method of using an ion exchange resin and an active alumina, a method of using a rare-earth compound as an adsorbent of fluorion, and a method of using a solution of a rare-earth compound and an alkali compound.
The Ca compound addition method uses Ca compounds, such as Ca(OH).sub.2 and CaCl.sub.2, single or in combination, to precipitate and separate the fluorion into water-insoluble CaF.sub.2. This method is most generally used as a high concentration fluorine processing method so far, which however requires a long-time processing. Also, reaction between the Ca compound and the fluorine is explained as a chemical equilibrium of acid and base between the reactants and products. A removal rate of the fluorine is also obtained up to a value expected from the chemical equilibrium constant (10 ppm at an optimal condition and 15 ppm in a general condition). Thus, it needs a large amount of chemicals to lower the concentration, which causes a large amount of sludges to occur.
The method of using an ion exchange resin and an active alumina which removes dissolved fluorion via the ion exchange, has a difficulty in removing a high concentration fluorine due to an exchange capacity of the ion exchange resin. Such a method can not process a large amount of wastewater and remove negative ions so that efficiency is lower when removing fluorine. Also, the process requires a high cost.
The method of using a rare-earth compound as a fluorion adsorbent adsorbs fluorion by exchanging the fluorion in the solution with hydroxide ion (OH.sup.-) contained in the rare-earth hydroxide. This method removes the fluorion at high efficiency up to several ppm or so, when compared with the others. However, a production cost of the rare-earth hydroxide is high and an equivalent weight of hydroxide ion (OH.sup.-) is lower than weight of added rare-earth hydroxide, which requires a large amount of chemicals in comparison with the fluorion to be processed. Also, since the exchange function is performed only in the acid solution, the pH of alkaline wastewater should be adjusted by an acid.
The method of adding soluble material composed of rare-earth compounds and making the fluorion insoluble to separate them is excellent in removing the fluorion even though the amount of chemicals used and the amount of the remaining sludges are small. However, the chemicals are expensive in price and the size of particle of the floating precipitate is small, it takes long time to precipitate them.
The above fluorion removal methods using the chemical process require a long-time processing, and a high processing cost due to a large amount of chemicals required, and produce a large amount of sludges. It is difficult to dispose the produced sludges. Thus, the above-described methods are not efficient for lowering the fluorion containing ratio down to a low concentration (several ppm). As a result, these conventional chemical processing methods are improper in countermeasuring environmental regulation. Finally, if these conventional chemical processing methods are used, an enormous amount of water is required for diluting the fluorion concentration which is not sufficiently low, so as to discharge the wastewater containing the fluorion.